Common reaction. The argument of the common liberal is so utterly seperated from reality that it baffles conservatives, AT FIRST. I would double-down and engage this guy as often as possible -- not to convert him, but to increase your ability to think on your feet.
Major suggestion is to question EVERY assumption. If this guy argues, it will often be from a starting assumption that is invalid. And, as you know, if you have a divide-by-zero anywhere in a proof, you can prove that 1=2.
Use him as a good sparring partner for when the real fights come, later in life.
I do from time to time. I don’t bring it up though. I have other friends that I spar with to keep me thinking coherently. It’s a long car ride. 35 min one way.
He lives on assumptions and random “studies”. I’ll say something and he’ll refute it with a random study that is done by elementary kids (not really, but he pulls them out of crazy places).
My all-time favorite comment of his was that He wouldn’t shoot to kill someone that was raping his mom or sister. You can’t argue with that. It’s illogical and stupid. No point in lowering myself to that line of thinking.